In recent years, various information-processing systems have been developed as the information technology industry has made rapid strides. Recording methods and recording devices suitable for such information-processing systems have also been developed, and each of them is in practical use.
Of those recording methods, an ink-jet recording method has been widely used not only in offices but also at home because of its advantages that various kinds of materials can be used for recording and the hardware (apparatus) used therein is relatively low in price, compact in size and excellent in quietness.
In addition, with recent improvements in resolution of ink-jet printers it has become possible to obtain records of the so-called photograph-like print quality, and these recent advances of hardware (apparatus) have stimulated the development of various types of ink-jet recording materials.
In general the properties required for recording sheets used in ink-jet recording include properties of being able to ensure (1) rapid drying of ink (sufficient rapidity of ink absorption), (2) ink dots of proper and uniform diameter (no ink bleed), (3) satisfactory graininess, (4) ink dots of high roundness, (5) high color densities, (6) high saturation (no color subsidence), (7) satisfactory imperviousness to water, light and ozone in printed areas, (8) high whiteness in themselves, (9) satisfactory keeping quality in themselves (occurrence of neither yellow coloration even in storage over a prolonged period nor image blur due to long-term storage (ageing-induced blur)), (10) high resistance to deformation and satisfactory dimensional stability (sufficiently loose curling), and (11) satisfactory hard-running performance.
In using photographic high-gloss paper for the purpose of obtaining records of the so-called photograph-like quality, glossiness, surface smoothness and a photographic-paper feeling similar to that of silver salt photograph are required in addition to the aforementioned properties.
For the purpose of improving those various properties, ink-jet recording materials having porous structures in their ink-receiving layers have been developed in recent years, and put to practical use. By having porous structures, these ink-jet recording materials can achieve high ink receptivity (fast-drying property) and high glossiness.
For instance, JP-A-10-119423 and JP-A-10-217601 propose the ink-jet recording materials wherein their individual supports are each provided with an ink-receiving layer having a high porosity by containing a particulate inorganic pigment and a water-soluble resin.
Because of their makeup, those recording materials, notably the ink-jet recording material provided with an ink-receiving layer of porous structure using silica as a particulate inorganic pigment, have excellent ink absorption and high ink-receiving power capable of forming images of high resolution, and can show high glossiness.
On the other hand, when recorded images of high optical densities are formed, it is known that a problem of the so-called bronzing phenomenon comes up, namely a phenomenon in which the dyes in ink crystallize out on the surface of a recording material as the ink dries; as a result, the recorded images reflect light and take on a metallic luster. This phenomenon is more likely to occur when the dye solubility in water is lowered or a hydrogen bond-forming group is introduced into the dye structure with the intention of enhancing water resistance, light resistance or gas resistance. Since reflection and scattering of light is caused by the bronzing phenomenon, the optical densities of images are lowered, and besides, the recorded images come to have hues significantly different from the intended ones or lost their transparency. Therefore, inhibition of the bronzing phenomenon is one of important requirements for ink-jet ink.
Examples of a hitherto known method for inhibition of the bronzing phenomenon include the methods for size control (as disclosed in JP-A-8-108616, JP-A-8-169173, JP-A-8-267908 and JP-A-2001-64893), the method of adding a specified heterocyclic compound (See JP-A-2001-88430), the method of adding a specified amine compound (See JP-A-2000-53765) and the method of adding a specified salt (See JP-A-2000-309156). However, there may be cases wherein the addition of those additives in increased amounts is required because of their insufficient effects in preventing the bronzing phenomenon from occurring, or the addition of those additives causes a storage-stability problem; as a result, the additives cause deteriorations in various properties of a recording medium and in recorded-image quality.
Although the use of additives can produce various effects as mentioned above, it is difficult to use usual additives while keeping various properties. For instance, when an image-receiving paper is designed to enhance weather resistance of recorded images through acceleration of dye association, the addition of an additive capable of loosening the dye association with the intention of preventing the occurrence of the bronzing phenomenon seriously impairs the keeping quality of recorded images even though it yields an improvement in the bronzing phenomenon. So it is understandable that there are difficulties in choosing amounts and kinds of additives to be added in such a case as to require a consideration of dye-associated conditions in particular. When ionic additives are used, on the other hand, it is required to take account of the influences of counter ions. Therefore, it has been desired to develop molecular designs of additives on the basis of a new concept and to introduce a method of inhibiting in a substantial sense the bronzing phenomenon by use of the additives developed.
Included among inkjet recording methods are a method of jetting liquid droplets under pressure applied thereto by an piezoelectric element, a method of jetting liquid droplets by thermally evolving bubbles in ink, a method of utilizing ultrasonic waves or a method of sucking and jetting liquid droplets by electrostatic force. As ink compositions for these inkjet recording methods, water-base ink, oil-base ink and solid (heat-fusion type) ink are usable. Of these ink varieties, water-base ink is the mainstream of inkjet recording ink from the viewpoints of production, handling, odor and safety.
Coloring materials used in ink compositions for inkjet recording are required to have a wide variety of properties including high solubility in solvents, high possibility for high-density recording, good hues, high fastness to light, heat, air, water and chemicals, firm fixation to image-receiving materials and resistance to spreading, excellent keeping quality in ink form, no toxicity, high purity and availability at low prices. However, it is extremely difficult to pursue coloring agents capable of satisfying those requirements at high levels.
Although various dyes and pigments were already proposed as coloring materials for inkjet recording and used practically, coloring materials meeting all the requirements are not found yet as matters now stand. And it is difficult to achieve both hue and fastness at the levels required for inkjet recording ink by use of well-known dyes and pigments to which color index (C.I.) numbers are assigned.
As dyes capable of enhancing fastness, JP-A-55-161856 proposes the azo dyes derived from aromatic amines and 5-membered heterocyclic amines. However, these dyes have undesirable hues in the yellow and cyan regions, so they have a problem of aggravating color reproduction.
JP-A-61-36362 and JP-A-2-212566 disclose the ink compositions for use in inkjet recording with the invention of achieving both hue and light fastness. However, the dyes adopted in each reference are insufficient in water solubility for use in water-base ink. In addition, when the dyes described in each reference are used in water-base ink for inkjet recording, the resulting ink has a problem with fastness to moisture and heat.
As means for solving those problems, the compounds and the ink composition described in JP-T-11-504958 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application) are proposed. For further improvements in hue and light fastness, the use of a pyrazolylanilineazo dye in the ink composition for inkjet recording is described in JP-A-2003-231850. However, those ink compositions for inkjet recording are insufficient in color reproduction and fastness of output images.
Images recorded with inkjet printers are generally stored in a state that the dyes constituting the images are unprotected, so their keeping quality is a disadvantage of them, in contrast to those recorded in photographic materials. Further, increasing an image recording speed in inkjet recording is generally performed by using a porous image-receiving material with the intention of enhancing ink absorbency. However, the use of a porous material has problems of lowering the glossiness and aggravating the fastness. Furthermore, it has turned out that the inkjet recording system using a porous image-receiving material has problems that a great hue change occurs immediately after printing and it takes a long time to completely stabilize the printed images.